Since the emergence of the resist for a KrF excimer laser (248 nm), it has been of common practice to employ a pattern forming method in which chemical amplification is utilized in order to compensate for any sensitivity decrease caused by light absorption. For example in a positive chemical amplification method, first, a photoacid generator contained in exposed areas is decomposed by light irradiation to thereby generate an acid. Then, in the stage of, for example, the bake after the exposure (Post-Exposure Bake: PEB), the generated acid exerts a catalytic action so that the alkali-insoluble group contained in the photosensitive composition is converted to an alkali-soluble group. Thereafter, development is carried out using, for example, an alkali solution. Thus, the exposed areas are removed to obtain a desired pattern.
For use in the above method, various alkali developers have been proposed. For example, an aqueous alkali developer containing 2.38 mass % TMAH (aqueous solution of tetramethylammonium hydroxide) is generally used.
The wavelength shortening of the exposure light source and the realization of high numerical apertures (high NA) for projector lenses have been advanced in order to cope with the miniaturization of semiconductor elements. To now, an exposure unit using an ArF excimer laser of 193 nm wavelength as a light source has been developed. Further, a method in which the space between a projector lens and a sample is filled with a liquid of high refractive index (hereinafter also referred to as an “immersion liquid”), namely liquid-immersion method has been proposed as a technology for enhancing the resolving power. Still further, an EUV lithography in which exposure is carried out using an ultraviolet of further shorter wavelength (13.5 nm) has been proposed.
However, the current situation is that it is extremely difficult to discover an appropriate combination of resist composition, developer, rinse liquid, etc., required for the formation of a pattern realizing comprehensively excellent performance. In particular, in accordance with the decrease of the resolved line width of resists, there is a demand for an enhancement of line pattern roughness performance and an enhancement of pattern dimension in-plane uniformity.
In this current situation, in recent years, various formulations have been proposed as a positive resist composition (see, for example, patent references 1 to 4). Moreover, the development of negative resist compositions for use in the pattern formation by alkali development is progressing (see, for example, patent references 5 to 8). These reflect the situation in which in the production of semiconductor elements and the like, while there is a demand for the formation of a pattern with various configurations, such as a line, a trench and a hole, there exist patterns whose formation is difficult with the use of current positive resists.
In recent years, also, a pattern forming method using a negative developer, namely, a developer containing an organic solvent is being exploited (see, for example, patent references 9 to 11). For example, patent reference 11 discloses a pattern forming method comprising the operations of applying onto a substrate a positive resist composition that when exposed to actinic rays or radiation, increases its solubility in a positive developer and decreases its solubility in a negative developer, exposing the applied resist composition and developing the exposed resist composition using a negative developer. This method realizes the stable formation of a high-precision fine pattern.
However, as for the composition described above, there is still a demand for further enhancements of the etching resistivity and the stability during a post-exposure delay (PED) period from exposure to post-bake.